Graduate Thesis Or Dissertation
 

Asulam in western Oregon pastures : broadleaf dock control and tolerance of important grass and legume species

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  • In previous research in Europe, asulam (methyl sulfanilylcarbamate) was found to be a potentially useful herbicide for controlling broadleaf dock Rumex obtusifolius L. ) in permanent pastures. Asulam was also reported to have a low margin of safety when used on common pasture species. Field studies were conducted in western Oregon to examine broadleaf dock control obtained at asulam rates that would not reduce pasture yield and to determine the optimum time of asulam application for dock control. Field, greenhouse, and laboratory studies were conducted to determine the tolerance of perennial ryegrass, tall fescue, orchardgrass, bentgrass, white clover, and subclover to asulam and to examine a possible change in protein content of grass forage after asulam application. Control of broadleaf dock was studied at three rates and four application times of asulam. Asulam was applied at 1. 0, 1. 5, and 2. 0 lb/A in April, May, June, and July. Results from early applications were superior to later applications of asulam. The April treatments were applied to dormant or slowly growing dock in the crown period. Control was good at all rates. The May treatments were made to actively growing dock late in the crown period or early in the rising period. Season-long control was good, but control of regrowth was not acceptable, particularly at the lower rates. June and July asulam treatments gave poor control of broadleaf dock at all rates. Pasture species differed in tolerance to asulam. Perennial ryegrass was the most tolerant grass and white clover was the most tolerant legume examined. Perennial ryegrass, tall fescue, orchardgrass, and white clover showed adequate tolerance to asulam, especially at the 1. 0 and 2. 0 lb/A rates. These species suffered slight yield decreases at 4. 0 lb of asulam/A. Bentgrass and subclover were less tolerant to asulam. These species suffered more severe injury and yield reduction at all rates of asulam than did the other species. Field studies also showed that clipping affected pasture grass tolerance to asulam. The effect of clipping was greatest in grass species that were most tolerant to asulam treatment. Clipping before asulam application increased injury to the sward. Injury increased as the period between clipping and treatment decreased. Clipping after asulam application reduced injury to the sward and increased speed of recovery. Laboratory experiments were conducted to determine the effect of asulam on the crude protein of tall fescue. Asulam caused a temporary reduction in the rate of crude protein loss. This coincided with a temporary growth delay observed in tall fescue after treatment. Asulam did not reduce the crude protein content of tall fescue at any harvest dates examined. Asulam can successfully control broadleaf dock in western Oregon pastures when applied at 1. 0 to 2. 0 lb/A in early spring with little or no damage to swards containing a large percentage of tolerant pasture species. Swards containing a large percentage of bentgrass and subclover should not be treated with asulam unless serious yield reductions can be accepted.
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